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Employee Benefit Plans - Schedule of Non-Vested Stock Awards (Detail) - Non-Vested Stock Awards [Member] - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Balance, Shares / Units 4,843,273 7,467,065 7,542,096
Granted, Shares / Units 5,152,082 1,496,408 2,195,638
Vested, Shares / Units (2,020,812) (3,840,379) (2,033,263)
Forfeited, Shares / Units (297,441) (279,821) (237,406)
Balance, Shares / Units 7,677,102 4,843,273 7,467,065
Balance, Weighted Average Market Value Per Share $ 31.66 $ 29.08 $ 22.53
Granted, Weighted Average Market Value Per Share 40.11 29.24 36.80
Vested, Weighted Average Market Value Per Share 29.75 25.09 21.29
Forfeited, Weighted Average Market Value Per Share 32.85 28.62 26.10
Balance, Weighted Average Market Value Per Share $ 37.76 $ 31.66 $ 29.08